1. Field of the Invention
This invention relates to a conveyor for conveying workpieces such as semiconductor wafers existing inside a vacuum chamber.
2. Description of the Prior Art
A conventional conveyor of this kind has a cylindrical separator wall 1 as shown in FIG. 5, and one of the ends of this separator wall 1 is open to the inside of a vacuum chamber 2 with the other end being closed by a cover 3.
A floating body 5 having a conveying rod 4 is disposed at the inner peripheral portion of the separator wall 1, and a driving unit 6 is fitted movably to the outer peripheral portion of the separator wall 1. The driving unit 6 is so constituted as to be capable of reciprocating along the outer peripheral portion of the separator wall 1 by a ball screw mechanism 8 disposed on a base 7.
Two sets of magnetic bearing portions 9, 9 are disposed inside the driving unit 6. Each of the magnetic bearing portions 9, 9 includes a plurality of electromagnets 10, 10 and a sensor portion not shown in the drawing. The sensor portion detects the floating position of the floating body 5. Each of the electromagnets 10 is excited on the basis of the detected value outputted from the sensor portion, and is constituted so that its magnetic force acts on the floating body 5 through the separator wall 1. In this way, each magnetic bearing portion 9, 9 supports the floating body 5 like a two-point support beam by magnetism.
In the conveyor described above, the floating body 5 is in advance supported by each magnetic bearing portion 9, 9, and the ball screw mechanism 8 is then driven so as to reciprocate the driving portion 6 along the outer periphery of the separator wall 1. The floating body 5 reciprocates in such a manner as to follow the reciprocation of the driving portion. Accordingly, the conveying rod 4 of the floating body 5 is constituted so as to convey a wafer W.
However, while the transfer of the wafer W by the conveying rod 4 described above can be attained by merely reciprocating the floating body 5, the conventional conveyor must drive the driving portion 6 when the floating body 5 reciprocates. Therefore, the size of the apparatus becomes greater by the moving space required for the driving portion 6 and by the installation space required for the ball screw mechanism 8 for moving the driving portion. Moreover, since the conventional ball screw mechanism 8 generates dust, the separator wall 1 is necessary and hence, the size of the apparatus becomes even greater.